1. Field of the Invention
This invention relates to a radiation image read-out apparatus for reading out a radiation image stored on a stimulable phosphor sheet by exposing the stimulable phosphor sheet to stimulating rays which cause the stimulable phosphor sheet to emit light in proportion to the stored radiation energy, and photoelectrically detecting the emitted light.
2. Description of the Prior Art
When certain kinds of phosphors are exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays, or ultraviolet rays, they store a part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted by the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in U.S. Pat. No. 4,258,264 and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use a stimulable phosphor in a radiation image recording and reproducing system. Specifically, a sheet provided with a layer of the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet) is first exposed to a radiation passing through an object such as the human body to have a radiation image of the object stored thereon, and then is scanned by stimulating rays such as a laser beam which cause the stimulable phosphor sheet to emit light in proportion to the stored radiation energy. The light emitted by the stimulable phosphor sheet upon stimulation thereof is photoelectrically detected and converted to electric image signals, and the radiation image of the object is reproduced as a visible image by use of the image signals on a recording medium such as a photographic film, a display device such as a cathode ray tube (CRT), or the like.
The radiation image recording and reproducing system using a stimulable phosphor sheet is advantageous over conventional radiography using a silver halide photographic material in that the image can be recorded over a very wide range (latitude) of radiation exposure. More specifically, since the amount of light emitted upon stimulation after the radiation energy is stored on the stimulable phosphor varies over a wide range in proportion to the amount of the stored energy, it is possible to obtain an image having desirable density regardless of the amount of exposure of the stimulable phosphor sheet to the radiation, by reading out the emitted light with an appropriate read-out gain and converting it into electric signals to reproduce a visible image on a recording medium or a display device.
In the aforesaid radiation image recording and reproducing system, the radiation image read-out is performed generally by use of a read-out apparatus for conveying the stimulable phosphor sheet in a sub-scanning direction, and scanning stimulating rays in a main scanning direction approximately normal to the sub-scanning direction.
In the read-out apparatus wherein the light emitted by the stimulable phosphor sheet in proportion to the stored radiation energy is detected by carrying out the sub-scanning and the main scanning, in order to detect the emitted light such that no image nonuniformity arises, it is necessary to provide a conveyance means for accurately conveying the stimulable phosphor sheet in the sub-scanning direction and a complicated optical system for accurately carrying out the main scanning. As the sub-scanning and main scanning are necessary, the conventional read-out apparatus is large-scaled, the mechanism of the apparatus is complicated, and therefore the cost of the apparatus becomes high.
On the other hand, the aforesaid radiation image recording and reproducing system may be used also for obtaining a radiation image of a small object for non-destructive inspection, dentistry, or the like. In this case, a small stimulable phosphor sheet is utilized, and it is desired that the image read-out be carried out without a large-scale read-out apparatus having a complicated mechanism being used as in the conventional technique.